Laser irradiation apparatus

ABSTRACT

An object is to obtain an even energy distribution of a laser beam in one direction, thereby conducting a uniform laser annealing on a film. 
     A laser irradiation apparatus comprising: a lens for dividing a laser beam in one direction; and an optical system for overlapping the divided laser beam, characterized in that the shape of the laser beam entering into the lens has edges vertical to the above-mentioned direction.

DETAILED DESCRIPTION OF THE INVENTION

1. Technical Field to which the Invention Belongs

The present invention relates to a technique capable of irradiating alarge area with a laser beam having high uniformity, and also theinvention relates to an application method thereof.

2. Prior Art

In recent years, extensive studies have been made on techniques in whichlaser annealing is performed on a non-single crystal semiconductor film(an amorphous semiconductor film which is not a single crystal, or asemiconductor film having crystallinity such as a polycrystalline andmicrocrystalline, and a semiconductor film in which thesecrystallinities are mixed) formed on an insulating substrate such asglass, to crystallize the film or to improve its crystallinity. Asilicon film is often used for the above semiconductor film.

As compared with a quartz substrate that has been conventionallyfrequently used, the glass substrate has such advantages that it isinexpensive, it is superior in workability, and a large substrate can beeasily formed. This is the reason why the above-mentioned researches arecarried out. Further, the reason why a laser is preferably used forcrystallization resides in that the melting point of the glass substrateis low. The laser is capable of giving high energy to only thesemiconductor film without varying the temperature of the substrate verymuch.

Since a crystalline silicon film formed by performing a laser annealingto a silicon film has high mobility, it is used in such a manner thatthin film transistors (TFTs) are formed with this crystalline siliconfilm, and are employed for, for example, a monolithic liquid crystalelectrooptical device in which a TFT for driving pixels and a TFT fordriver circuits are formed on one glass substrate. Since the crystallinesilicon film is made of a large number of crystal grains, it is alsocalled a polycrystal silicon film or a polycrystal semiconductor film.

A method in which a pulse laser beam of an excimer laser or the likehaving high output is processed by an optical system so that a squarespot of several cm or a linear shape of several hundred μm×several tenscm is formed on a surface to be irradiated, and the laser beam is madeto scan (irradiation position of the laser beam is relatively moved tothe irradiated surface) to make laser annealing, is superior in massproductivity and excellent in industry, so that the method is used bypreference.

Particularly, when a linear laser beam is used, differently from thecase of using a spot-like laser beam which requires back-and-forth andright-and-left scanning, laser irradiation to the whole irradiatedsurface can be made by scanning in only the direction normal to the linedirection of the linear laser. Thus, high mass productivity can beobtained. The reason why scanning is made in the direction normal to theline direction is that it is the most effective scanning direction. Bythis high mass productivity, at present, laser annealing using thelinear laser beam has become the mainstream.

Problem to be Solved by the Invention

When laser annealing is performed to the non-crystal semiconductor filmby scanning of the laser beam that has been processed into a linearshape, rectangular, or square, some problems have occurred. One ofespecially serious problems among them is that the processing of laserbeam is not uniformly carried out. When such a linear laser beam isused, laser annealing is nonuniformly performed onto the whole surfaceof the substrate.

FIG. 1 is a photograph of an optical microscope showing a state that alaser beam that has been processed into a linear shape by using aconventional optical system, is irradiated by one shot onto an amorphoussilicon film. It can be observed irradiation marks at the center of thephotograph.

FIG. 1 shows a case that an XeCl excimer laser having a wavelength of308 nm is processed into a linear laser beam extending in theright-and-left direction on the paper surface, and is irradiated by oneshot onto the amorphous silicon film.

It can be confirmed from FIG. 1 that edges in the width direction of thelinear laser beam, particularly, an edge on the lower side of the papersurface has indentation, thereby being a linear laser beam having anuneven energy distribution.

FIG. 2 a is a view schematically showing a state where a laser beam 201having the uneven energy distribution shown in FIG. 1 is irradiated on afilm 209.

As shown in FIG. 2 a, a region 202 having a high energy density isformed at a center of the width direction, and regions 203 having alower energy density compared to the region 202 are formed at peripheralportions of the width direction. FIGS. 2 b and 2 c each show sectionalshapes of the energy distribution taken along the line X-X′ and Y-Y′ ofFIG. 2 a.

From FIGS. 2 a to 2 c, it can been seen that a laser beam 201 hasdifferent sectional shapes of the energy distribution in the widthdirection.

Laser annealing is performed onto the film by using the laser beam 201of FIG. 2 a, however, uniform laser annealing of the film can not becarried out.

The invention disclosed in the present specification has an objectthereof to uniform the energy distribution in one direction of the laserbeam, thereby uniformly performing the laser annealing of the film.Throughout the specification, “laser beam” indicates a region of 5% ormore of the maximum energy within the laser beam.

Process Lead to the Invention

In general, in the case where a laser beam is processed into a linearshape, an originally substantially rectangular beam is made to passthrough a suitable optical system and is processed into the linearshape. Although the aspect ratio of the substantially rectangular beamis about 2 to 5, for example, by an optical system shown in FIG. 3, itis transformed into the linear beam having an aspect ratio of 100 ormore. At that time, the optical system is designed such that thedistribution of energy in the beam is also homogenized at the same time.

The apparatus shown in FIG. 3 has a function to irradiate a laser beam,as a linear beam, from a laser beam generating unit 301 (in this state,the shape of the beam is substantially rectangular) through opticalsystems represented by 302, 303, 304, 306, and 308. Note that referencenumeral 305 denotes a slit, and 307 denotes a mirror.

Reference numeral 302 denotes an optical lens serving to divide a laserbeam in one direction, a linear direction in this case, and acylindrical lens group (also referred to as a multicylindrical lens) isused. The divided many beams are overlapped and homogenized with respectto the linear direction by the cylindrical lens 306.

This structure is required to improve the strength distribution in thelaser beam. The cylindrical lens group 303 also divides the laser beamin another direction, the width direction in this case, like theforegoing cylindrical lens group 302, and the divided beams areoverlapped and homogenized with respect to the width direction by thecylindrical lenses 304 and 308.

That is, the combination of the cylindrical lens group 302 and thecylindrical lens 306 has a function to improve the strength distributionin the line direction of the linear laser beam, and the combination ofthe cylindrical lens group 303 and the cylindrical lenses 304 and 308has a function to improve the strength distribution in the widthdirection of the linear laser beam.

In this case, with respect to the width direction, two cylindricallenses 304 and 308 are used to make finer in the width direction of thelinear laser beam on the irradiated surface 309. According to the widthof the linear laser beam, the number of optical systems for overlappingmay be made one, or may be made three or more.

The optical system serving to homogenize the energy distribution in thelaser beam is referred to as a beam homogenizer. The optical systemshown in FIG. 3 is also one of beam homogenizers. After thesubstantially originally rectangular laser beam is divided by thecylindrical lens groups 302 and 303, the divided beams each are shapedand overlapped by the cylindrical lenses 306, 304 and 308 to homogenizethe energy distribution thereof.

Theoretically speaking, if the energy distribution of the laser beam ismade even using a cylindrical lens group that includes infinite numbersof cylindrical lenses, a uniform laser beam can be obtained no matterwhat sectional shape the entered laser beam has.

However, in an industrially applicable cylindrical lens group, several,several tens at most, cylindrical lenses are used in consideration ofits precision, cost, etc. In the cylindrical lens group as such, a laserbeam is processed into a laser beam having an irregular energydistribution due to a sectional shape of the entered laser beam and thecondition of entrance.

The present inventors have found that this unevenness, which hasconventionally been considered as not much a trouble, causes a lot ofproblems mentioned above when that laser is used in laser annealing on afilm represented by a thin film transistor (TFT) where minute elementsare formed on the same substrate in a large number.

FIGS. 4 a and 4 b shows an example of, in a beam homogenizer forprocessing a laser into a linear laser beam, a cylindrical lens group403 for dividing a laser beam in the width direction and a laser beam401 entered thereto.

As shown in FIGS. 4 a and 4 b, laser beams 401, 401′ emitted from thebeam generating unit 301 in FIG. 3 and entered into the optical systemfor dividing the laser beams have a substantially rectangular shape inits cross section.

Laser beams to be emitted from the beam generating unit 301 are ideallyemitted with a perfect rectangular shape. However, it is realisticallyimpossible with technologies present, and the sectional shapes thereofbecome substantially rectangular shapes.

In FIG. 4 a, the laser beam is not entered over the entire width of thecylindrical lens in a cylindrical lens 4031 on the top and a cylindricallens 4036 on the bottom. In addition, the entered beam shape isirregular.

On the other hand, the laser beam is entered over the entire width ofeach lens in four cylindrical lenses 4032 to 4035 placed therebetween.

FIG. 5 is a structural diagram showing an optical system for processingwith respect to its width direction, taken out from the optical systemfor processing linear laser beams. As shown in FIG. 5, when a laser beam501 is to be entered into a cylindrical lens group 503 in a manner shownin FIG. 4A, the laser beam enters to cylindrical lenses 5031 and 5036with its edge irregular, not straight.

For that reason, the laser beams divided by the cylindrical lenses 5031and 5036 are overlapped with each other on an irradiated surface 509while the laser beams maintain the irregular shape by cylindrical lens504. Thus formed is a linear beam that is not homogenous in the lineardirection, namely a beam having an energy distribution whose sectionalshape in the width direction varies in accordance with linear direction.

Then it becomes, for example, a linear laser beam in which a region 202having a high energy density as shown in FIG. 2 a is formed near thecenter in the width direction, and regions 203 having a lower energydensity as compared to the region 202 are formed on the periphery in thewidth direction.

When the laser beam 401′ is to be entered to a cylindrical lens group403′ for dividing the laser beam in the width direction as shown in FIG.4 b, a laser beam having an irregular shape enters to a cylindrical lens4035,′ resulting in, similarly, a linear laser beam that is nothomogenous in linear direction.

From the facts above, the present inventors have found out thefollowings. The cause of non-uniform laser annealing by a laser beamlies in an irregularly shaped laser beam that enters to some cylindricallenses of a cylindrical lens group for dividing the laser beam. Becauseof this, the energy distribution of the linear laser beam becomesirregular.

Means for Solving the Problem

According to one aspect of the present invention, there is provided alaser irradiation apparatus comprising: a lens for dividing a laser beamin one direction; and an optical system for overlapping the dividedlaser beams, characterized in that a shape of a laser beam entering intothe lens has edges vertical to the direction.

Further, according to another aspect of the present invention, there isprovided a laser irradiation apparatus comprising: a beam generatingunit; a lens for dividing a laser beam in one direction; and an opticalsystem for overlapping the divided laser beams, characterized in that aslit is formed between the beam generating unit and the lens, forforming edges in the laser beam, which is vertical to the direction.

Still further, according to another aspect of the present invention,there is provided a laser irradiation apparatus comprising: an opticalsystem for dividing a laser beam in one direction; and an optical systemfor overlapping the divided laser beams, characterized in that, in thedirection, a width of the optical system for dividing is narrower thanthe maximum width of the laser beam before being divided.

Yet further, according to another aspect of the present invention, thereis provided a laser irradiation apparatus comprising: a cylindrical lensgroup for dividing a laser beam in one direction; and an optical systemfor overlapping the divided laser beams, characterized in that a portionof the cylindrical lens of the cylindrical lens group is shielded.

EMBODIMENT MODE OF THE INVENTION

One embodiment mode of the present invention will be described withreference to FIG. 6. FIG. 6 shows, for simplification, only ahomogenizer relative to the width direction in an apparatus forprocessing a linear laser beam.

Besides, in the following descriptions, a laser beam with substantiallyrectangular shape in its cross section at an emission is exemplified.However, the feature of the present invention resides in the sectionalshape of the laser beam to be processed. Accordingly, any kind of laserbeam with any sectional shape at the emission may be applicable.However, in order to efficiently use the energy of the laser beam, alaser beam with a rectangular shape is preferred to a circular or anelliptical one.

The periphery of a substantially rectangular laser beam 601 is cut withthe use of a slit 610, forming a rectangular laser beam. With the slit610, the formerly irregular edge of the laser beam is processed so as tobe a straight line. In addition, the slit 610 is arranged so that thestraight line is vertical to the direction along which the beam isdivided by a cylindrical lens group 603 (width direction).

Then, the laser beam enters to an optical system for dividing thisrectangular laser beam, here, the cylindrical lens group 603. For theslit 610, glass, quartz ground glass, ceramic, metal, etc. may be used,and particularly preferred is light-shielding with the quartz groundglass. This is because quartz is not decomposed by the laser beam, andhardly produces substances harmful to semiconductor manufacture.

The laser beam usable in the present invention is not limited to excimerlaser beams such as KrF, XeCl, ArF and KrCl, but Ar laser, YAG laser,CO2 laser and other various laser beams may be used. The excimer laserincludes a continuous light emission excimer laser as well as a pulseoscillation excimer laser.

At this point, the edge vertical to the direction along which therectangular laser beam is divided, i.e., the longer sides of therectangular in FIG. 6, are set in parallel with the boundaries betweenthe cylindrical lenses of the cylindrical lens group. Also, the shortersides of the rectangular are set in parallel with the boundaries betweenthe cylindrical lenses of the cylindrical lens group for dividing thebeam in the linear direction, though not shown.

The laser beam entered to the cylindrical lens group 603 is divided inone direction and divided beams are overlapped with each other on anirradiated surface 609 by a cylindrical lens 604. In this way, a laserbeam homogenous in linear direction, although having the high energydensity region 202 and the low energy density regions 203, can beobtained.

When the laser beam processed with the slit into a rectangular of whichedge is straight enters to the cylindrical lens group, the longer sidesof the rectangular are made coincident with the boundaries between thecylindrical lenses of the cylindrical lens group or with the ends of thecylindrical lens group for dividing in the width direction, and theshorter sides of the rectangular are made coincident with the boundariesbetween the cylindrical lenses of the cylindrical lens group or with theends of the cylindrical lens group for dividing the beam in lineardirection. By doing so, the high energy density region in the linearlaser beam may be enlarged as compared to the case where the sides donot coincide with the boundaries or the ends.

Therefore, the laser beam may be processed to have a large area (to belonger if it is linear), improving productivity. Note that the highenergy density region in this matter designates a region having anenergy density equal to or larger than the energy density required forlaser annealing.

Further, the energy distribution of the linear laser beam is almosthomogenized in regions except for the beam ends. More uniform laserannealing is therefore possible.

On the other hand, as shown in FIG. 6, when at least one of edgesvertical to the direction along which the laser beam is divided does notcoincide with the boundaries between the cylindrical lenses of thecylindrical lens group or with the ends of the cylindrical lens group,upon entrance of the laser beam processed into a rectangular with theslit to the cylindrical lens group, a linear laser beam having aplurality of energy densities is obtained.

Another embodiment may be given in which the width in the directionalong which an entered laser beam is divided is set wider than the widthin the dividing direction of an optical system for dividing.

FIG. 7 shows an example thereof. In FIG. 7, a cylindrical lens group 703includes, for instance, quartz ground glass as replacement forcylindrical lenses 7031, 7036 to which, if in the prior art, anirregularly shaped laser beam is entered. This shields light and makeswider the width of the laser beam in the direction along which the beamis divided than the width of an optical system for dividing (cylindricallenses 7032 to 7035) in the dividing direction. A substantiallyrectangular laser beam 701 entered thus can have straight edges.

Though only a homogenizer relative to the width direction of the laserbeam is shown in FIG. 7, for simplification, it is preferable to use asimilarly structured optical system for dividing also with respect tothe linear direction.

As a simpler method, the straight edge may be obtained by making widerthe width of the entered laser beam 701 in the direction that the beamis divided than the width of the dividing optical system 703 itself inthe dividing direction.

Then, the divided laser beams are overlapped on an irradiated surface709 with the cylindrical lens 704. The laser beam thus processed canhave an even energy distribution in the direction along which it isdivided and, in addition, an enlarged region of high energy density.

In this way, the periphery of the substantially rectangular laser beamis cut to form the rectangular laser beam. However, the portion to becut is preferably as small as possible in order to prevent energy lossof the laser beam.

It is also preferred to arrange the optical system so that as largeportion of the high energy density region as possible, which is aroundthe center of the laser beam, is entered to the optical system fordividing the laser beam.

The laser beam having a plurality of energy densities on the irradiatedsurface may have various shapes by controlling the condition of entranceto the cylindrical lens group for dividing the laser beam. For instance,the laser beam can have energy distribution of: a convex shape, as shownin FIG. 9 a, consisting of three regions different in energy densityfrom one another with the middle rectangular region the highest; aconcave shape, as shown in FIG. 9 b, consisting of three regionsdifferent in energy density from one another with the middle rectangularregion the lowest; or a combined shape, as shown in FIG. 9 c, consistingof two regions different in energy density from each other.

FIG. 8 shows an example of a laser irradiation apparatus using thepresent invention. A substantially rectangular laser beam irradiatedfrom a beam generating unit 801 is processed into a linear shape,through reflecting mirrors 802, by optical systems 803, 808.

A reflecting mirror 807 reflects the direction of the laser beam towarda processed substrate 809. Although the reflecting mirror 807 is notalways necessary, it is provided to make the laser irradiation apparatuscompact. An example of an optical system in which no reflecting mirror807 is provided is shown in FIG. 21, and an examples of an opticalsystem in which a position is changed at which the reflecting mirror isbrought in is shown in FIG. 22.

An irradiation stage 805 holding the processed substrate 809 can bemoved relative to the width direction of the linear laser beam. In thelaser irradiation apparatus shown in FIG. 8, such a structure is adoptedthat the irradiation stage is moved. However, such a structure may beadopted that the linear laser beam is moved.

However, when the linear laser beam is moved, the energy distribution isapt to change, so that there is a fear that the laser annealing becomesuneven. Thus, it is preferable that the irradiation stage is moved.

The optical system 803 includes an optical system processing the laserbeam in the linear direction, and an optical system dividing the laserbeam in the width direction. The optical system 808 serves to overlapthe laser beams divided in the width direction on the same plane.

The role of the reflecting mirror 802 will be described below. Thedirection of the laser beam emitted from a beam generating unit 801 ischanged subtly each time when the maintenance of the laser irradiationapparatus is conducted. Therefore, it is difficult to make the laserbeam directly incident on the lens provided to the optical system 803,as the light beam vertical and parallel to the lens.

Therefore, a reflecting mirror 802 is arranged at an emitting port ofthe laser generating unit and an angle of the reflecting mirror 802 isadjusted, so that the direction of the laser beam may be finelyadjusted. As a result, the laser beam can be made incident on theoptical system 803 while substantially parallel thereto.

In the above, the beam homogenizer for processing the laser beam intothe linear laser beam, and the laser irradiation apparatus using suchthe beam homogenizer have been explained.

Moreover, the foregoing beam homogenizer can also be applied to not onlythe case of processing the laser beam into a linear shape, but also thecase of processing the laser beam into a rectangular or square shapewith an aspect ratio of 100 or less.

In such the laser irradiation apparatus, as shown in FIG. 6, a slit 610is arranged between the optical system for dividing the laser beam andthe beam generating unit, and the periphery of the laser beam with asubstantially rectangular shape is cut to form a rectangular laser beamwith edges of straight lines.

In addition, the laser beam may be processed into square other thanprocessing into rectangular by cutting all the peripheries of the laserbeam with the slit 610. It is also possible to cut only a part of theperiphery by means of the slit. At that occasion, as described later, atleast an incident of the laser beam having an irregular shape on theoptical system for dividing the laser beam in the width direction isrequired to be eliminated.

Further, as means for eliminating the incident of the laser beam havingirregular shape on the optical system for dividing the laser beam, therecan be employed a method in which in place of the slit 610, the width inthe direction along which an entered laser beam is divided is set widerthan the width in the dividing direction of an optical system fordividing. As an example thereof, as shown in FIG. 7, there is a methodin which a part of cylindrical lenses in the cylindrical lens group isshielded from light.

In this method, it is preferably applied to both cylindrical lens groupsfor dividing the laser beam in the width direction and for dividing inthe linear direction. However, in the case where the linear laser beamis formed, the shielding is required to be applied at least to thecylindrical lens group for dividing the laser beam in the widthdirection.

In the linear laser beam, at least the laser beam with an irregularshape must be eliminated from entering into the optical system fordividing the laser beam in the width direction. The reason thereofresides in that when the laser annealing is performed, in the case ofthe linear laser beam, the irradiated substrate is relatively moved tothe direction vertical to the linear direction, that is, to the widthdirection. Accordingly, the variation of energy distribution in thewidth direction results in nonuniform laser annealing over all thesurface of the substrate.

On the other hand, the incident of the irregular beam on the opticalsystem for dividing the laser beam in the linear direction hardlyinfluences on the energy distribution at the center portion of thelinear laser beam. Accordingly, if the center portion only is used,industrial application thereof is available.

In the case where scanning is performed on the irradiated surface byusing a laser beam having a rectangular shape or a square shape, if thelength of one side of the laser beam having a rectangular shape or asquare shape (the length of the longer side in case of rectangular) islonger than the length of the short side of the substrate, similarly tothe linear laser beam, laser annealing is completed by scanning in onlyone direction.

However, in the case where the length of the rectangular or square laserbeam in the long side direction is shorter than the length of the shortside of the substrate, it is necessary to make scanning of therectangular or square laser beam at plural times, with the result that amechanism for moving the irradiation stage becomes complicate.

The irradiated substrate is not limited to a glass substrate, but aquartz substrate, a ceramic substrate, a semiconductor substrate, aplastic substrate, an organic resin substrate, or the like may beemployed. Particularly, it is effective to use the laser annealingagainst the glass substrate, the plastic substrate, or the organic resinsubstrate.

An example of the use of the laser beam to which the present inventionis applied, resides in the crystallization of films having a crystalstructure such as amorphous, polycrystal, and microcrystal, or in theimprovement of the crystallinity of the film. The “improvement of thecrystallinity” means the fact that the crystal structure of the filmobserved by Raman spectroscopy analysis etc. further approaches tosingle crystal. However, the present inventor found, separately from theresult obtained by Raman spectroscopy analysis, that the electric fieldmobility of a film is increased by laser annealing. Accordingly, thedefinition of the “improvement of crystallinity” includes the increasein this electric field mobility.

In addition, the laser beam to which the present invention is applied,can be used for activating impurities that have been added to the films,or for the laser annealing for recovering the disorder in the crystalstructure due to ion injection, and the like.

Premising such uses, the present invention is particularly effective fora film containing silicon as a main component. However, it is needlessto say that the film to be irradiated in the present invention is notlimited to a particular film.

When YAG laser is used for the purpose of crystallizing a filmcontaining silicon as a main component, a wave length having at leastone of the second to the fourth harmonic waves is used. Further, whenYAG laser is used for the purpose of activating or/and laser annealing,a wave length containing one or a plurality of the basic wave to thefourth harmonic waves is used.

Shown in the following embodiments is an example of the presentinvention, and the present invention is not particularly limit to theembodiments. For example, a semi-cylindrical lens group is used for theoptical system for dividing the laser beam, to thereby reduce aninfluence of a spherical aberration. As a result, the present inventioncan be used for processing a laser beam so as to have a verticalsectional shape at the ends of the energy distribution on the irradiatedsurface.

EMBODIMENT Embodiment 1

FIG. 10 is a photograph of an optical microscopy showing a state where alaser beam processed into a linear shape is irradiated onto an amorphoussilicon film by one shot using a laser irradiation apparatus of FIG. 8.It can be observed marks of the laser beam irradiation at the center ofthe photograph.

FIG. 10 is a case where an XeCl excimer laser having a wave length of308 nm is processed into a linear laser beam having a width of 500 μmextending in right-and-left direction of a paper surface, and this laserbeam is irradiated on the amorphous silicon film.

A linear beam used in FIG. 10 has been processed by using an opticalsystem in which a part of quartz cylindrical lens of the cylindricallens group of the optical system used for dividing the laser beam in thewidth and linear directions is replaced with quartz ground glass. Withthis, entrance of a laser beam having an irregular shape into theoptical system for dividing the laser beam has been prevented.

It can be confirmed, from FIG. 10, that by cutting the periphery of thelaser beam having a substantially rectangular shape, energy distributionin the linear direction of the linear laser beam becomes uniform.

FIG. 11 is a view schematically showing FIG. 10. As shown in FIG. 11,edges, formed by a linear laser beam 1101, between a high energy densityregion 1102 and low energy density regions 1103 are straight lines. Thisshows the sectional shapes of the energy distributions in the widthdirection are equal in any portion. Note that in the present embodiment,the reason why the regions 1103 are produced, causes the precision ofmachining the lens or the precision of positioning the lens.

However, compared to that of FIG. 1 and FIG. 2, the high energy densityregion 1102 becomes extremely wider, thereby being capable of uniformlylaser annealing.

Embodiment 2

The present embodiment is an example in which laser annealing is usedupon manufacturing a polycrystal silicon film. First, a method ofmanufacturing a film to be irradiated with laser will be described. Thefilms to be irradiated with laser are the following three kinds of filmsin the present specification. The present invention is effective for anyfilm.

In any of three kinds of the films, first, a Corning 1737 glasssubstrate of 127 mm square is used as a substrate, and a silicon nitridefilm with a thickness of 200 nm or more is formed thereon as an underfilm for preventing the diffusion of impurities from the substrate, by aplasma CVD method in which silane and ammonia are used as the startinggases. Heat treatment is then subjected thereto to improve the filmquality.

Further, the second under film and an amorphous silicon film arecontinuously formed (subsequent film formation is carried out after theformer film formation without exposing to air) by the plasma CVD method.As the second film, a silicon oxide film (SiOx), silicon nitride film(SiNx) or silicon nitride oxide film (SiOxNy) is formed to have athickness of 10 to 100 nm. In this embodiment, 50 nm of silicon oxidefilm is formed. An amorphous silicon film is formed to have a thicknessof 10 to 100 nm. In this embodiment, 50 nm of the amorphous silicon filmis formed thereon by a plasma CVD method. This amorphous film will behereinafter referred to as a starting film.

(Manufacturing Procedure of Film A)

The starting film is subjected to heat bathing at 450° C. for one hour.This step is for reducing the hydrogen concentration in the amorphoussilicon film. If hydrogen in the film is excessively high, the film cannot resist the laser energy, so that this step is required.

The density of hydrogen in the film is suitably the order of 10²⁰atoms/cm³. This dehydrogenized amorphous silicon film will be referredto as a non-single crystal silicon film A.

(Manufacturing Procedure of Film B)

A nickel acetate solution of 10 ppm is applied to the starting film by aspin coating method to form a nickel acetate layer. It is morepreferable to add a surfactant to the nickel acetate solution. Since thenickel acetate layer is very thin, although it is not always film-like,a problem does not occur in the subsequent steps.

Next, the substrate on which each film is laminated in the mannerdescribed above is subjected to thermal annealing at 600° C. for 4hours. Then, the amorphous silicon film is crystallized, so that acrystalline silicon film B of a non-single crystal silicon film isformed.

At this time, nickel as a catalytic element functions as nuclei ofcrystal growth, so that crystallization is accelerated. By the functionof nickel, crystallization can be made at a low temperature for a shorttime such as 600° C. and 4 hours. The details are disclosed in JapanesePatent Application Laid-open No. Hei. 6-244104.

It is preferable that the concentration of the catalytic element is1×10¹⁵ to 1×10¹⁹ atoms/cm³. When the concentration is as high as 10¹⁹atoms/cm³ or more, metallic properties appear in the crystalline siliconfilm, and the semiconductor characteristics are lost. In the presentembodiment, the concentration of the catalytic element in thecrystalline silicon film is 1×10¹⁷ to 10¹⁸ atoms/cm³. These values areobtained by analysis and measurement with secondary ion massspectroscopy (SIMS).

(Manufacturing Procedure of Film C)

A silicon oxide film with a thickness of 700 nm is further formed on thestarting film. A plasma CVD method is used as a film formation method.

Next, a part of the silicon oxide film is completely opened by aphotolitho patterning step.

Further, for the purpose of forming a thin oxide film on the openingportion, irradiation of UV light is carried out in an oxygen atmospherefor 5 minutes. This thin oxide film is formed to improve wettability ofthe opening portion to a subsequently introduced nickel solution.

Next, a nickel acetate solution of 100 ppm is applied to the film by aspin coating method, so that nickel acetate enters the opening portion.It is more preferable to add a surfactant into the nickel acetatesolution.

Next, thermal annealing at 600° C. for 8 hours is carried out, so thatcrystal grows from the nickel introduced portion in the lateraldirection. At this time, the role of nickel is the same as in the filmB. In the condition at this time, about 40 μm as a lateral growth amountis obtained.

In this way, the amorphous silicon film is crystallized, so that acrystalline silicon film C of a non-single crystal silicon film isformed. Thereafter, the silicon oxide film on the non-single crystalsilicon film C is peeled and removed by using buffered hydrofluoricacid.

Laser annealing using an excimer laser is applied to the non-singlecrystal silicon films A, B, and C obtained in this way.

FIG. 8 shows a laser irradiation apparatus in the present embodiment.FIG. 8 shows the outline of the laser irradiation apparatus.

In FIG. 8, a laser beam is radiated from a laser beam generating unit801, and after the traveling direction of the laser beam is adjusted byreflecting mirrors 802, the beam is processed by optical systems 803 and808 so that its sectional shape is made linear. A reflecting mirror 807reflects the laser beam, so that a processed substrate 809 is irradiatedwith the laser beam. A beam expander which suppresses an expanding angleof the laser beam and can adjust the size of the beam may be insertedbetween the reflecting mirrors 802.

Then, an irradiation stage 805 holding the processed substrate 809 canbe moved in the width direction of the linear laser beam.

In the optical system 803 according to the present embodiment, the slit610 is provided, as shown in FIG. 6, at immediately before the opticalsystem for dividing the laser beam between the optical system fordividing the laser beam and the beam generating unit, to cut theperiphery of the entered laser beam so as to form a rectangular shape.

By using such apparatuses, processing of the laser beam as describedbelow was carried out.

As the laser beam generating unit 801, the unit for oscillating XeClexcimer laser (wavelength 308 nm) is used. Other than this, excimerlaser such as KrF excimer laser (wavelength 248 nm), ArF (wavelength 193nm), KrCl (wavelength 222 nm), and the like may be used. Also, Ar laser,YAG laser having at least one of the second to the fourth harmonicwaves, etc. may be used.

The size of the laser beam emitted from the beam generating unit isabout 15 mm×45 mm at immediately before the optical system for dividingthe laser beam.

The size of the slit arranged at immediately before the optical systemfor dividing the laser beam is 12 mm×35 mm. As a result, the peripheryof the laser beam is cut to form a rectangular shape.

Then, edges vertical to the direction along which the laser beam isdivided are made parallel with the boundaries between the cylindricallenses of the cylindrical lens group for dividing the laser beam.

As the cylindrical lens group for dividing the laser beam in the lineardirection, a cylindrical lens group in which seven cylindrical lenseseach made of synthesis quartz with a width of 5 mm are arranged inparallel to each other is used.

As the cylindrical lens group for dividing the laser beam in the widthdirection, a cylindrical lens group in which six cylindrical lenses eachmade of synthesis quartz with a width of 2 mm are arranged in parallelto each other is used.

The cylindrical lens group is arranged so that the center thereof isaligned with the center of a laser beam.

The laser beams thus divided pass through the optical lens foroverlapping the laser beams, and are processed into a width of 0.1 to 1mm and a length of 100 to 300 mm on the processed substrate 809. In thepresent embodiment, a linear laser beam with a width of 0.4 mm and alength of 135 mm is obtained.

Here, the shorter sides of the rectangular are made coincident with theends of the cylindrical lens group in the linear direction. Also, thelonger sides of the rectangular laser beam are made coincident with theends of the cylindrical lens group in the width direction. By doing so,the laser beam can be obtained in which the sectional shape of theenergy distribution of the laser beam on the irradiated surface isrectangular.

Next, an apparatus shown in FIG. 12 will be described. A cassette 1203in which a number of, for example, 20 processed substrates 809 arecontained is disposed in a load/unload chamber 1205. One substrate istransferred from the cassette 1203 by a robot arm 1204 into an alignmentchamber 1202.

In the alignment chamber 1202, an alignment mechanism for correcting thepositional relation between the processed substrate 809 and the robotarm 1204 is disposed.

The substrate is transferred into a substrate transfer chamber 1201 bythe robot arm 1204, and further, transferred into a laser irradiationchamber 1206 by the robot arm 1204.

In FIG. 8, the linear laser beam radiated onto the processed substrate809 has 0.4 mm in width×135 mm in length.

The energy density of the laser beam at the irradiated surface is in therange of 100 mJ/cm² to 500 mJ/cm², for example, 350 mJ/cm²in the presentembodiment. The irradiation stage 805 is moved in one direction at 1.2mm/s so that the linear laser beam is made to scan.

The oscillation frequency of the laser is 30 Hz, and when an attentionis paid to one point of the irradiated object, 10 shots of the laserbeams are applied. The number of shots is suitably selected in the rangefrom 5 shots to 50 shots.

After the end of the laser irradiation, the processed substrate 809 isreturned to the substrate transfer chamber 1201 by the robot arm 1204.

The processed substrate 809 is transferred to the load/unload chamber1205 by the robot arm 1204 and is stored in the cassette 1203.

With this, the laser annealing step is ended. In this way, the foregoingstep is repeated, so that a number of substrates can be continuouslyprocessed one by one.

In the laser irradiation system in FIG. 12, in order to minimize thespace of the apparatus, a load/unload chamber 1205 is served by onechamber. However, to increase productivity, it may take a structure inwhich unload chamber is provided separately.

In that case, such a structure may be employed for the improvement ofthe productivity in which a second alignment chamber is provided to asubstrate transferring chamber 1201 and the unload chamber connected tothe second alignment chamber is provided. However, if such a structureis employed in which the second substrate transferring chamber isarranged at a laser irradiation chamber 1206, and the processedsubstrates after the completion of the laser irradiation are transferredto the second alignment chamber and the unload chamber with a robot armof the second substrate transferring chamber, further effect on theproductivity may be obtained.

In the present embodiment, although the linear laser beam is used, evenif any beam shape from the linear shape to the square is used, theeffect of the feature of the present invention is obtained.

As the result that the non-single crystal films A, B, and C weresubjected to laser annealing by using this laser irradiation apparatus,in the non-single crystal silicon film A, it was possible to obtain auniform laser crystallized polycrystal silicon film over the wholesurface of the substrate.

In the non-single crystal silicon films B and C, the crystallinity ofthe silicon film over the whole surface of the substrate was furtherpromoted, so that it was possible to obtain a polycrystal silicon filmhaving a high electric field effect mobility compared to that beforelaser annealing.

When the polycrystal silicon film obtained in accordance with thepresent embodiment is utilized as semiconductor layers including asource, a drain, and a channel region of TFT that functions as aswitching element of a liquid crystal display or an organic EL display,it can be obtained the one in which the mark caused by the laserprocessing is not noticeable compared with the prior art.

Embodiment 3

In the present embodiment, as a method for cutting the periphery of alaser beam having a substantially rectangular shape, a cylindrical lensof a cylindrical lens group of an optical system for dividing the laserbeam is shielded from light to which a laser beam having an irregularshape is entered.

When employing the method shown in Embodiment 2, the shorter sides andthe longer sides of the rectangular slit need to be arranged in parallelwith the respective dividing directions. There is a fear thatmisalignment in the arrangement causes entrance of an irregularly shapedlaser beam into the optical system for dividing. This embodiment,however, can solve the problem above, as the cylindrical lenses in theoptical system for dividing to which an irregularly shaped laser beamenters are shielded against light.

This embodiment uses a laser irradiation apparatus having the structureobtained by removing the slit 601 from the laser irradiation apparatusin Embodiment 2 and by shielding some cylindrical lenses of thecylindrical lens group being shielded against light.

The size of the laser beam emitted from a beam generating unitimmediately before the optical system is about 15 mm×45 mm.

As the cylindrical lens group for dividing the laser beam in the widthdirection, a cylindrical lens group in which eight cylindrical lenseseach made of synthesis quartz with a width of 2 mm are arranged inparallel to each other is used. The cylindrical lens group is arrangedso that the center thereof is aligned with the center of an enteredlaser beam, and both ends of the cylindrical lenses are shielded byquartz ground glass. As a result, periphery in the width direction ofthe entered laser beam can be cut.

As the cylindrical lens group for dividing the laser beam in the linedirection, a cylindrical lens group in which nine cylindrical lenseseach made of synthesis quartz with a width of 6 mm are arranged inparallel to each other is used. The cylindrical lens group is arrangedso that the center thereof is aligned with the center of an enteredlaser beam, and both ends of the cylindrical lenses are shielded byquartz ground glass. As a result, periphery in the line direction of theentered laser beam can be cut.

In this way, in the present embodiment, the width of the optical systemfor dividing the laser beam is made shorter than the width of the laserbeam with respect to its dividing direction. As a result, periphery ofthe laser beam can be cut.

The cylindrical, lenses on both ends of the cylindrical lens group areshielded against light in this embodiment. Alternatively, a cylindricallens group whose width is shorter than the width of a laser beam to beentered with respect to the dividing direction may be used. In thatcase, a light-shielding plate is preferably placed around thecylindrical lens group in order to cut a part of the laser beam which isnot entered. Also, the cylindrical lens group may be supported by thelight-shielding plate.

The laser beam thus divided is, after passing through the optical systemfor overlapping, processed to have a width of 400 μm and a length of13.5 cm on a processed substrate.

As the result that the non-single crystal films A, B, and C weresubjected to laser annealing by using this laser irradiation apparatus,in the non-single crystal silicon film A, it was possible to obtain auniform laser crystallized polycrystal silicon film over the wholesurface of the substrate.

Also, in the non-single crystal silicon films B and C, the crystallinityof the silicon film over the whole surface of the substrate was furtherpromoted, so that it was possible to obtain a polycrystal silicon filmhaving a high mobility compared to that before laser annealing.

When the polycrystal silicon film obtained in accordance with thepresent embodiment is utilized as semiconductor layers including asource, a drain, and a channel region of TFT that functions as aswitching element of a liquid crystal display or an organic EL display,it can be obtained the one in which the mark caused by the laserprocessing is not noticeable compared with the prior art.

Embodiment 4

In the present embodiment, a laser beam is divided by using acylindrical lens group shorter than the width of the laser beam, and acylindrical lens to which the laser beam having an irregular shape isentered, is eliminated.

Besides, the laser irradiation apparatus of this embodiment adopts thestructure in which a combination cylindrical lens group is used for theoptical system of the beam homogenizer in the width direction to reducethe aberration of the lens. Adoption of such a structure makes itpossible to reduce a blur region to 25 μm or less in the energydistribution in the width direction on the surface to be irradiated witha linear laser beam, and to bring the edge thereof to nearly vertical.The blur region refers to a region of which energy is 90 to 5% of themaximum.

FIG. 8 shows a laser irradiation apparatus according to the presentembodiment. FIG. 8 is an outer appearance of the laser irradiationapparatus.

In the laser irradiation apparatus in FIG. 8, a laser beam is emittedfrom a laser beam generating unit 801 and, after adjustment is made onits traveling direction by reflecting mirrors 802, processed to have alinear sectional shape by optical systems 803, 808. A reflecting mirror807 reflects a pulse laser beam to irradiate a processed substrate 809with the laser beam. A beam expander that can keep the angle of thelaser beam from being wide and can adjust the size of the beam may beinserted between the reflecting mirrors 802.

An irradiation stage 805 holding the processed substrate can move in thewidth direction of the linear laser beam.

The optical system 803, the reflecting mirror 807, and the cylindricallens 808 in accordance with the present embodiment have the structuresshown in FIG. 13.

In FIG. 13, the incident laser beam is divided in the linear directionby a cylindrical lens group 1402, and is divided in the width directionby a combination cylindrical lens group 1403 of convex meniscuscylindrical lens and a planoconvex cylindrical lens.

In the present embodiment, although the structure shown in FIG. 13 isused as the optical lens for dividing the laser beam in the widthdirection. However, such a structure may be employed that anothercombination cylindrical lens group, or a cylindrical lens group in whichalmost all aberration is eliminated by processing lenses into asphericlenses may be used, for reducing the blur region and making the edgeswith a nearly vertical shape.

Then the laser beams divided by an optical lens 1404 made of a triplettype symmetrical lens are overlapped and homogenized, and the laserbeams are overlapped on the processed substrate 1409 relative to thewidth direction through a slit 1405 and a cylindrical lens 1406 and byan optical lens 1408 made of a Tessar type symmetrical lens.

In the present embodiment, although the symmetrical lens is used as theoptical lenses 1404 and 1408, another combination lens may be used, orsuch a structure that aberration is almost eliminated by making anaspheric lens may be adopted.

Beside, the slit 1405 is not necessarily required, and is used foradjusting the width of the linear laser beam.

With the above-mentioned apparatus, the processing of the laser beamdescribed below is carried out.

As the laser beam generating unit 801, in this case, the unitoscillating XeCl excimer laser (wave length 308 nm) is used.Alternately, KrF excimer laser (wave length 248 nm), ArF (wave length193 nm), KrCl (wave length 222 nm), etc. may be used.

The length in the width direction of the laser beam emitted from thelaser irradiation apparatus was about 16 mm. The laser beam is madeincident on the optical lens for dividing the laser beam in the widthdirection.

As the optical lens, such a structure 1403 is employed that acylindrical lens group in which seven cylindrical lenses each made ofsynthesis quartz with a width of 2 mm are arranged in parallel to eachother and a cylindrical lens group in which seven cylindrical lenseshaving a convex-convex plane each made of synthesis quartz with a widthof 2 mm are arranged, are combined. In FIG. 13, only 4 stages of thecylindrical lens group are described for simplification.

As described above, the optical lens has a width of only 14 mm which issmaller than 16 mm of the width of the entered laser beam. Accordingly,the ends of the entered laser beam are not used.

Since the ends of the entered laser beam have nonuniform energy, inorder to enhance the uniformity of the laser beam, it is preferable notto use ends of the laser beam.

The laser beam thus divided in the width direction is processed to havea width of 300 to 1,000 μm on the substrate through an optical lens 1404and an optical lens 1408. The width of the laser beam can be adjusted byvarying the distance between the optical lenses 1404 and 1408.

The linear laser beam thus processed hardly receives the influence ofthe aberration of the lens with respect to the width direction.Accordingly, the linear laser beam having vertical edges of the energydistribution may be obtained.

In the present embodiment, the linear laser beam irradiated on theprocessed substrate 809 has a width of 0.4 mm×a length of 135 mm.

Energy density of the laser beam on the irradiated surface ranges from100 mJ/cm² to 500 mJ/cm². In this embodiment, it was set to 350 mJ/cm².While moving an irradiation stage 805 in one direction at 1.2 mm/s, thelinear laser beam is scanned.

The oscillation frequency of the laser is set to 30 Hz. An attention isgiven to one point of the object to be irradiated, 10 shots of laserbeam irradiation are performed thereon. The number of shot may beappropriately selected from 5 shots to 50 shots.

Thus laser annealing process is ended. By repeating the above-mentionedprocess in this manner, a large number of substrates can be continuouslyprocessed one by one.

Though the present embodiment uses a linear laser, any beam shape fromlinear to square can be applied to the present invention to obtain thesame effect that is a feature of the present invention.

As the result that the non-single crystal films A, B, and C weresubjected to laser annealing by using this laser irradiation apparatus,in the non-single crystal silicon film A, it was possible to obtain auniform laser crystallized polycrystal silicon film over the wholesurface of the substrate.

Also, in the non-single crystal silicon films B and C, the crystallinityof the silicon film over the whole surface of the substrate was furtherpromoted, so that it was possible to obtain a polycrystal silicon filmhaving a high mobility compared to that before laser annealing.

In addition, employment of the combination lens as the optical lens canprevent the phenomenon of stripes where the characteristics of TFTs areperiodically fluctuated. Comparing to the conventional optical systemsfor preventing the occurrence of stripes, the difference can beremarkably seen when an active matrix type liquid crystal display deviceor an organic EL display is manufactured in which the silicon filmobtained in accordance with the present invention is used as theswitching element.

In the present embodiment, although the symmetrical lenses are used asthe optical lenses 1404 and 1408, another combination lens may be used,or such a structure that aberration is almost eliminated by making anaspheric lens may be adopted.

In the present embodiment, although the combination lenses are used forthe optical lenses 1404 and 1408 to reduce aberration, even if only theoptical lens 1408 is made the combination lens, and the optical lens1404 is made a cylindrical lens single body, it is possible to relievethe stripe formation.

When a TFT having an active layer made of the laser annealed siliconfilm is manufactured, both of an N channel type and a P channel Type canbe manufactured.

Further, the structure of combination of an N channel type and a Pchannel type can also be obtained. Besides, a number of TFTs can also beintegrated to form an electronic circuit.

Although the non-single crystal silicon films A, B, and C are providedon the flat glass substrate, even if the formed surfaces of thenon-single crystal silicon films A, B, and C have uneven shapes due towiring or the like, the laser annealing is effective.

In the case where a liquid crystal display or an organic EL displayincluding TFTs is manufactured by using the semiconductor film subjectedto the laser annealing through the optical system of the presentinvention, a high quality display can be obtained in which fluctuationof characteristics of each TFT is low.

The above can also be applied to a semiconductor film subjected to laserannealing through optical systems indicated in other embodiments.

Embodiment 5

In the present embodiment, by using a laser beam processed into a squareshape of 10 mm×10 mm, the non-single crystal silicon films A, B, and Care subjected to laser annealing.

An optical system for processing a beam into a square shape is shown inFIG. 14. In the present embodiment, it is preferable that the directionof the incident laser beam is vertical to the cylindrical lens group1302 and semi-cylindrical lens group 1303.

The incident laser beam is divided in an X-axis direction by thecylindrical lens group 1302, and is divided in a Y-axis direction (theX-axis direction and the Y-axis direction correspond to the lineardirection and the width direction in the linear laser beam) by thesemi-cylindrical lens group 1303.

The divided laser beams are overlapped on the processed surface 1309 bya cylindrical lens 1306 with respect to the X-axis direction, and areoverlapped on the processed surface 1309 with respect to the Y-axisdirection by a cylindrical lens 1304.

Further, in a laser processing apparatus used in the present embodiment,an irradiation stage includes means for moving in two directions of theX-axis direction and the Y-axis direction.

By using the above optical system, the laser beam is processed into asquare of 10 mm×10 mm at the processed substrate, and the non-singlecrystal silicon films A, B and C are subjected to laser annealing. Theenergy density of the laser beam at the irradiated surface is made to350 mJ/cm2.

As a result, in the non-single crystal silicon film A, it was possibleto obtain a polycrystal silicon film in which the whole surface of thesubstrate was almost uniformly laser crystallized.

Further, in the non-single crystal silicon films B and C, thecrystallinity of the silicon films on the whole surface of the substratewas further promoted, and it was possible to obtain polycrystal siliconfilms having a high electric field effect mobility compared to thatbefore laser annealing.

Embodiment 6

This embodiment of the present invention will be described withreference to FIGS. 15 to 18. Here, a description will be made on amethod of manufacturing a pixel portion and a driver circuit provided onthe periphery of the pixel portion of a liquid crystal display device atthe same time using a semiconductor film obtained in Embodiments 1 to 3.However, for simplifying the description, with respect to the drivercircuit, a CMOS circuit as a basic circuit of a shift register circuit,a buffer circuit, and the like, and an n-channel TFT forming a samplingcircuit will be shown.

In FIG. 15(A), it is desirable to use a glass substrate or a quartzsubstrate as a substrate 3100. Other than those, a substrate obtained byforming an insulating film on the surface of a silicon substrate, ametal substrate, or a stainless substrate may be used. A plasticsubstrate may also be used so far as the heat resistance permits.

An under film 3101 made of an insulating film containing silicon (inthis embodiment, this insulating film generically denotes a siliconoxide film, a silicon nitride film, or a silicon nitride oxide film) andhaving a thickness of 100 to 400 nm is formed by a plasma CVD method ora sputtering method on the surface of the substrate 3100 on which a TFTis to be formed. Note that the silicon nitride oxide film in thisembodiment is an insulating film expressed by SiOxNy, and denotes aninsulating film containing silicon, oxygen, and nitrogen at apredetermined ratio.

In this embodiment, the under film 3101 was formed of a two-layerstructure of a silicon nitride oxide film with a thickness of 25 to 100nm, here, 50 nm, and a silicon oxide film with a thickness of 50 to 300nm, here, 150 nm. The under film 3101 is provided to prevent impuritycontamination from the substrate, and in the case where the quartzsubstrate is used, the under film does not have to be always provided.

Next, a semiconductor film (in this embodiment, an amorphous siliconfilm (not shown)) containing amorphous structure and having a thicknessof 20 to 100 nm is formed on the under film 3101 by a known filmformation method. Note that the semiconductor film containing amorphousstructure includes an amorphous semiconductor film and amicrocrystalline semiconductor film, and also, a compound semiconductorfilm containing amorphous structure, such as an amorphous silicongermanium film.

Then, in accordance with a technique disclosed in Japanese PatentApplication Laid-open No. Hei 7-130652 (corresponding to U.S. Pat. No.5,643,826), a semiconductor film 3102 containing crystal structure (inthis embodiment, a crystalline silicon film) is formed. The techniquedisclosed in the publication is crystallizing means using, whencrystallizing an amorphous silicon film, a catalytic element (one kindor plural kinds of elements selected from nickel, cobalt, germanium,tin, lead, palladium, iron, and copper, representatively nickel) forpromoting crystallization.

Specifically, the technique is such that a heat treatment is carried outin a state where a catalytic element is held on the surface of anamorphous silicon film, so that the amorphous silicon film istransformed into a crystalline silicon film. In this embodiment,although a technique disclosed in the embodiment 1 of the publication isused, a technique disclosed in the embodiment 2 may be used. Note thatalthough the crystalline silicon film includes a so-called singlecrystal silicon film and a polycrystalline silicon film, the crystallinesilicon film formed in this embodiment is a silicon film includingcrystal grain boundaries (FIG. 15(A)).

It is desirable to carry out the step of crystallization in such amanner that although depending on a hydrogen content, the amorphoussilicon film is preferably heated at 400 to 550° C. for several hours tocarry out a dehydrogenating treatment so that the hydrogen content islowered to 5 atom % or less. The amorphous silicon film may be formed byanother manufacturing method such as a sputtering method or anevaporation method, but it is desirable that impurity elements such asoxygen and nitrogen is sufficiently reduced.

Here, since the under film and the amorphous silicon film can be formedby the same film forming method, both may be sequentially formed. Thenthe under film is prevented from being exposed to the atmosphere onceafter the under film is formed, so that pollution on the surface can beprevented, and it is possible to reduce fluctuation in characteristicsof TFTs to be manufactured.

Next, by a method described in the embodiments 1 to 3, laser annealingis applied to the crystalline silicon film 3102 to form a crystallinesilicon film 3103 in which the crystallinity is improved. As laserlight, although pulsed oscillation or continuous-wave excimer laserlight is desirable, continuous-wave argon laser light may be used (FIG.15(B)).

In this embodiment, by using the optical system shown in the embodiment2, pulsed oscillation excimer laser light is converted into linear lightand a laser annealing step is carried out. The laser annealing conditionis such that a XeCl gas is used as an excitation gas, treatmenttemperature is adjusted to room temperature, the frequency of pulsedoscillation is set to 30 Hz, and the density of laser energy is set to250 to 500 mJ/cm² (representatively 350 to 400 mJ/cm²).

The laser annealing step carried out in the above condition has effectsto completely crystallize an amorphous region remaining after thermalcrystallization, and to reduce defects or the like of a crystallineregion which is already crystallized. Thus, this step may be called astep of improving crystallinity of a semiconductor film by lightannealing or a step of promoting crystallization of a semiconductorfilm. Such effects can also be obtained by optimizing the condition oflaser annealing. In this embodiment, such a condition is called a firstannealing condition.

Next, a protection film 3104 for subsequent impurity addition is formedon the crystalline silicon film 3103. A silicon nitride oxide film or asilicon oxide film with a thickness of 100 to 200 nm (preferably 130 to170 nm) is used as the protection film 3104. This protection film 3104has meanings to prevent the crystalline silicon film from being directlyexposed to plasma at impurity addition, and to enable delicateconcentration control.

Then a resist mask 3105 is formed thereon, and an impurity element forgiving p type (hereinafter referred to as a p-type impurity element) isadded through the protection film 3104. As the p-type impurity element,representatively an element belonging to group 13, typically boron orgallium may be used. This step (called a channel doping step) is a stepfor controlling a threshold voltage of a TFT. Here, boron is added by anion doping method in which diborane (B₂H₆) is not subjected to massseparation but is subjected to plasma excitation. Of course, an ionimplantation method using mass separation may be used.

By this step, an impurity region 3106 containing the p-type impurityelement (in this embodiment, boron) with a concentration of 1×10¹⁵ to1×10¹⁸ atoms/cm³ (representatively 5×10¹⁶ to 5×10¹⁷ atoms/cm³) isformed. In this embodiment, an impurity region containing a p-typeimpurity element within at least the above concentration range isdefined as a p-type impurity region (b) (FIG. 15(C)).

Next, the resist mask 3105 is removed, and resist masks 3107 to 3110 arenewly formed. Then an impurity element for giving n type (hereinafterreferred to as an n-type impurity element) was added to form impurityregions 3111 to 3113 exhibiting an n type. As the n-type impurityelement, representatively an element belonging to group 15, andtypically phosphorus or arsenic may be used (FIG. 15(D)).

The low concentration impurity regions 3111 to 3113 are impurity regionswhich are subsequently made to function as LDD regions in n-channel TFTsof a CMOS circuit and a sampling circuit. In the impurity regions formedhere, the n-type impurity element with a concentration of 2×10¹⁶ to5×10¹⁹ atoms/cm³ (representatively 5×10¹⁷ to 5×10¹⁸ atoms/cm³) iscontained. In this embodiment, an impurity region containing an n-typeimpurity element within the above concentration range is defined as ann-type impurity region (b).

Here, phosphorus with a concentration of 1×10¹⁸ atoms/cm³ is added by anion doping method in which phosphine (PH₃) is not subjected to massseparation but to plasma excitation. Of course, an ion implantationmethod using mass separation may be used. In this step, phosphorus isadded to the crystalline silicon film through the protection film 3104.

Next, the protection film 3104 is removed, and an irradiation step of alaser beam is again carried out by a method described in the embodiments1 to 3. In this embodiment, laser annealing is carried out by using theoptical system described in the embodiment 2. Although pulsedoscillation or continuous-wave excimer laser light is desirable as thelaser beam, continuous-wave argon laser light may be used. However,since an object thereof is activation of added impurity elements, it ispreferable to make irradiation with energy at such a level that thecrystalline silicon film is not melted. It is also possible to carry outthe laser annealing step while the protection film 3104 is keptremaining (FIG. 15(E)).

In this embodiment, pulsed oscillation excimer laser light is convertedinto linear light and the laser annealing step was carried out. Thelaser annealing condition was such that a KrF gas is used as anexcitation gas, treatment temperature is adjusted to room temperature,the frequency of pulsed oscillation is set to 30 Hz, and the density oflaser energy is set to 100 to 300 mJ/cm² (representatively 150 to 250mJ/cm²).

The laser annealing step carried out under the above condition haseffects to activate the added impurity elements for giving n type or ptype and to recrystallize the semiconductor film which has been madeamorphous at addition of the impurity elements. The above condition ispreferably such that atomic arrangement is aligned without melting thesemiconductor film, and the impurity elements are activated. This stepmay be called a step of activating an impurity element for giving n typeor p type by laser annealing, a step of recrystallizing a semiconductorfilm, or a step of carrying out both at the same time. In thisembodiment, such a condition will be referred to as a second annealingcondition.

By this step, boundary portions of the n-type impurity regions (b) 3111to 3113, that is, junction portions to intrinsic regions (the p-typeimpurity region (b) is also regarded as substantially intrinsic)existing around the n-type impurity regions (b) become definite. Thismeans that at the point of time when a TFT is subsequently completed,the LDD region and a channel formation region can form a very excellentjunction portion.

When the impurity element is activated by the laser beam, activation bya heat treatment may be employed together with it. In the case whereactivation by the heat treatment is carried out, the heat treatment atabout 450 to 550° C. is appropriate in view of the heat resistance ofthe substrate.

Next, unnecessary portions of the crystalline silicon film are removedand island-like semiconductor films (hereinafter referred to as activelayers) 3114 to 3117 are formed (FIG. 15(F)).

Next, a gate insulating film 3118 covering the active layers 3114 to3117 is formed. It is appropriate that the gate insulating film 3118 isformed to have a thickness of 10 to 200 nm, preferably 50 to 150 nm. Inthis embodiment, a silicon nitride oxide film with a thickness of 115 nmis formed by a plasma CVD method using N₂O and SiH₄ as a raw material(FIG. 16(A)).

Next, a conductive film to become a gate wiring line is formed. Althoughthe gate wiring line may be formed of a conductive film of a singlelayer, it is preferable to make a laminated film such as a two-layer orthree-layer film according to necessity. In this embodiment, a laminatedfilm made of a first conductive film 3119 and a second conductive film3120 is formed (FIG. 16(B)).

Here, as the first conductive film 3119 and the second conductive film3120, it is possible to use an element selected from tantalum (Ta),titanium (Ti), molybdenum (Mo), tungsten (W), chromium (Cr), and silicon(Si), a conductive film containing mainly the foregoing element(representatively, tantalum nitride film, tungsten nitride film,titanium nitride film), or an alloy film containing a combination of theforegoing elements (representatively, Mo—W alloy, Mo—Ta alloy).

It is appropriate that the thickness of the first conductive film 3119is 10 to 50 nm (preferably 20 to 30 nm), and the thickness of the secondconductive film 3120 is 200 to 400 nm (preferably 250 to 350 nm). Inthis embodiment, a tungsten nitride (WN) film with a thickness of 50 nmis used as the first conductive film 3119, and a tungsten film with athickness of 350 nm is used as the second conductive film 3120.

Although not shown, it is effective that a silicon film with a thicknessof about 2 to 20 nm is previously formed under the first conductive film3119. By this, it is possible to improve the adhesiveness of theconductive film formed thereon and to prevent oxidation.

Next, the first conductive film 3119 and the second conductive film 3120are etched at the same time to form gate wiring lines 3121 to 3124 witha thickness of 400 nm. At this time, the gate wiring lines 3122 and 3123formed in the driver circuit are formed to overlap with a part of then-type impurity regions (b) 3111 to 3113 through the gate insulatingfilm. This overlapping portion subsequently becomes a Lov region.Although the gate wiring line 3124 is seen double in section, it isactually formed of one continuously connected pattern (FIG. 16(C)).

Next, an n-type impurity element (in this embodiment, phosphorus) isadded by using the gate wiring lines 3121 to 3124 as masks in aself-aligning manner. It was adjusted such that phosphorus with aconcentration of ½ to 1/10 (representatively ⅓ to ¼) of that of then-type impurity region (b) (however, the concentration is 5 to 10 timesas high as the concentration of boron added in the foregoing channeldoping step, representatively 1×10¹⁶ to 5×10¹⁸ atoms/cm³, typically3×10¹⁷ to 3×10¹⁸ atoms/cm³) is added to the thus formed impurity regions3125 to 3130. Note that in this embodiment, an impurity regioncontaining an n-type impurity element within the above concentrationrange is defined as an n-type impurity region (c) (FIG. 16(D)).

Although phosphorus with a concentration of 1×10¹⁶ to 5×10¹⁸ atoms/cm³is added also to all the n-type impurity regions (b) except portionsconcealed with the gate wiring lines, since its concentration is verylow, it does not affect the function as the n-type impurity region (b).Besides, although boron with a concentration of 1×10¹⁵ to 1×10¹⁸atoms/cm³ is already added in the n-type impurity regions (b) 3127 to3130 at the channel doping step, in this step, since phosphorus with aconcentration 5 to 10 times as high as boron contained in the p-typeimpurity region (b) is added, it is permissible to consider that borondoes not affect the function of the n-type impurity region (b) in thiscase as well.

However, strictly, among the n-type impurity regions (b) 3111 to 3113,in contrast to the concentration of phosphorus in the portionoverlapping with the gate wiring line keeps 2×10¹⁶ to 5×10¹⁹ atoms/cm³,in the portion not overlapping with the gate wiring line, phosphoruswith a concentration of 1×10¹⁶ to 5×10¹⁸ atoms/cm³ is added thereto, sothat phosphorus with a slightly high concentration is contained.

Next, the gate insulating film 3118 is etched with the gate wiring lines3121 to 3124 as masks in a self-aligning manner. A dry etching method isused as etching, and a CHF₃ gas is used as an etching gas. However, itis not necessary to limit the etching gas to this. In this way, gateinsulating films 3131 to 3134 are formed under the gate wiring lines(FIG. 16(E)).

The active layers are exposed in this way, so that it is possible tolower an acceleration voltage when an adding step of impurity elementsis next carried out. Besides, since a necessary dosage can be made low,a throughput is improved. Of course, the gate insulating film may not beetched but remained to form an impurity region by through doping.

Next, resist masks 3135 to 3138 to cover the gate wiring lines areformed, and an n-type impurity element (in this embodiment, phosphorus)is added to form impurity regions 3139 to 3147 containing phosphoruswith a high concentration. Also in this case, an ion doping method (ofcourse, an ion implantation method may be used) using phosphine (PH₃) isused, and the concentration of phosphorus in the regions is 1×10²⁰ to1×10²¹ atoms/cm³ (representatively 2×10²⁰ to 5×10²¹ atoms/cm³) (FIG.16(F)).

Note that in this embodiment, an impurity region containing an n-typeimpurity element within the above concentration range is defined as ann-type impurity region (a). Although phosphorus or boron added in theformer step is already contained in the regions where the impurityregions 3139 to 3147 are formed, since phosphorus with a sufficientlyhigh concentration is added, the influence of phosphorus or boron addedin the former step does not have to be considered. Thus, in thisembodiment, it does not matter if the impurity regions 3139 to 3147 arerephrased by n-type impurity regions (a).

Next, the resist masks 3135 to 3139 are removed, and a resist mask 3148is newly formed. Then a p-type impurity element (in this embodiment,boron) is added to form impurity regions 3149 and 3150 containing boronwith a high concentration. Here, boron with a concentration of 3×10²⁰ to3×10²¹ atoms/cm³ (representatively 5×10²⁰ to 1×10²¹ atoms/cm³) is addedby an ion doping method using diborane (B₂H₆) (of course, an ionimplantation method may be used). Note that in this embodiment, animpurity region containing a p-type impurity element within the aboveconcentration range is defined as a p-type impurity region (a) (FIG.17(A)).

Although phosphorus with a concentration of 1×10²⁰ to 1×10²¹ atoms/cm³is added in a part of the impurity regions 3149 and 3150 (foregoingn-type impurity regions (a) 3139 and 3140), boron added here is addedwith a concentration at least 3 times as high as that. Thus, thepreviously formed n-type impurity regions are completely inverted intop-type, and function as p-type impurity regions. Thus, in thisembodiment, it does not matter if the impurity regions 3149 and 3150 arerephrased by p-type impurity regions (a).

Next, after the resist mask 3148 is removed, a first interlayerinsulating film 3151 is formed. The first interlayer insulating film3151 is appropriately formed of an insulating film containing silicon,specifically, a silicon nitride film, a silicon oxide film, a siliconnitride oxide film, or a laminated film containing a combination ofthose films. The film thickness is appropriately 100 to 400 nm. In thisembodiment, a silicon nitride oxide film (concentration of nitrogen is25 to 50 atomic %) having a thickness of 200 nm and formed by a plasmaCVD method with SiH₄, N₂O, NH₃ as a raw material gas is used.

Thereafter, a heat treatment step for activating the n-type or p-typeimpurity element added in each concentration is carried out. This stepcan be carried out by a furnace annealing method, a laser annealingmethod, or a rapid thermal annealing method (RTA method). Here, althoughan activating step is carried out by the furnace annealing method, it isalso effective to use laser annealing described in the embodiments 1 to3. A heat treatment is performed at 300 to 650° C., preferably 400 to550° C., here, 550° C. for four hours in a nitrogen atmosphere (FIG.17(B)).

At this time, in this embodiment, the catalytic elements (in thisembodiment, nickel) used for crystallization of the amorphous siliconfilm move in the directions indicated by arrows, and are captured(gettered) in the regions which are formed in the above step of FIG.16(F) and containing phosphorus with a high concentration. This is aphenomenon caused by a gettering effect of phosphorus for a metalelement, and as a result, in subsequent channel formation regions 3152to 3156, the concentration of the catalytic element became 1×10¹⁷atoms/cm³ or less (preferably 1×10¹⁶ atoms/cm³ or less).

Conversely, in the regions which became gettering sites of the catalyticelement (regions where the impurity regions 3139 to 3147 are formed inthe step of FIG. 16(F)), the catalytic element with a high concentrationis segregated and the catalytic element with a concentration of 5×10¹⁸atoms/cm³ or more (representatively, 1×10¹⁹ to 5×10²⁰ atoms/cm³) come toexist.

Further, a heat treatment at 300 to 450° C. for 1 to 12 hours is carriedout in an atmosphere containing hydrogen of 3 to 100%, and a step ofhydrogenating the active layers is carried out. This step is a step ofterminating dangling bonds in the semiconductor layer by thermallyexcited hydrogen. As other means of hydrogenating, plasma hydrogenating(using hydrogen excited by plasma) may be carried out.

After the activating step is completed, a second interlayer insulatingfilm 3157 with a thickness of 500 nm to 1.5 μm is formed on the firstinterlayer insulating film 3151. In this embodiment, a silicon oxidefilm with a thickness of 800 nm is formed as the second interlayerinsulating film 3157 by a plasma CVD method. In this way, an interlayerinsulating film having a thickness of 1 μm and made of the firstinterlayer insulating film (silicon nitride oxide film) 3151 and thesecond interlayer insulating film (silicon oxide film) 3157 is formed.

As the second interlayer insulating film 3157, an organic resin film ofpolyimide, acrylic resin, polyamide, polyimideamide, BCB(benzocyclobutene) or the like may be used.

Thereafter, a contact hole reaching a source region or drain region ofeach TFT is formed, and source wiring lines 3158 to 3161, and drainwiring lines 3162 to 3165 are formed. Although not shown, for thepurpose of forming the CMOS circuit, the drain wiring lines 3162 and3163 are connected as the same wiring line. Besides, although not shown,in this embodiment, this electrode is made to have a three-layerstructure laminated film in which a Ti film with a thickness of 100 nm,an aluminum film containing Ti and having a thickness of 300 nm, and aTi film having a thickness of 150 nm are continuously formed by asputtering method.

Next, as a passivation film 3166, a silicon nitride film, a siliconoxide film, or a silicon nitride oxide film is formed to have athickness of 50 to 500 nm (representatively, 200 to 300 nm). At thistime, in this embodiment, prior to formation of the film, a plasmatreatment using a gas containing hydrogen, such as H₂ or NH₃, is carriedout, and a heat treatment is carried out after the film formation.Hydrogen excited by this preliminary treatment is supplied to the firstand second interlayer insulating films. By carrying out the heattreatment in this state, the film quality of the passivation film 3166is improved, and it is possible to effectively hydrogenate the activelayer since hydrogen added in the first and second interlayer insulatingfilms is diffused to the under layer side.

Besides, after the passivation film 3166 is formed, a hydrogenating stepmay be further carried out. For example, it is appropriate that a heattreatment at 300 to 450° C. for 1 to 12 hours is carried out in anatmosphere containing hydrogen of 3 to 100%. Alternatively, also when aplasma hydrogenating method was used, the same effect is obtained. Here,at a position where a contact hole for connecting a pixel electrode tothe drain wiring line is subsequently formed, an opening portion may beformed in the passivation film 3166.

Thereafter, a third interlayer insulating film 3167 made of organicresin and having a thickness of about 1 μm is formed. As the organicresin, polyimide, acryl, polyamide, polyimideamide, BCB(benzocyclobutene) or the like can be used. As merits of using theorganic resin film, there are cited a point that a film forming methodis simple, a point that parasitic capacity can be reduced since relativedielectric constant is low, a point that excellent flatness is obtained,and the like. Note that an organic resin film other than those mentionedabove, organic SiO compound, and the like can also be used. Here,polyimide of a type that is thermally polymerized after application tothe substrate is used and fired at 300° C. to form the film.

Next, in the region to be a pixel portion, a shielding film 3168 isformed on the third interlayer insulating film 3167. Note that in thisembodiment, the word “shielding film” is used to carry the meaning ofshielding against light and electromagnetic waves.

As the shielding film 3168, a film made of an element selected fromaluminum (Al), titanium (Ti), and tantalum (Ta) or a film containingeither one of those elements as its main ingredient is formed to have athickness of 100 to 300 nm. In this embodiment, an aluminum filmcontaining titanium of 1 wt % and having a thickness of 125 nm wasformed.

Note that when an insulating film made of a silicon oxide film or thelike and having a thickness of 5 to 50 nm is formed on the thirdinterlayer insulating film 3167, it is possible to improve theadhesiveness of the shielding film formed thereon. Besides, when aplasma treatment using a CF₄ gas is applied to the surface of the thirdinterlayer insulating film 3167 formed of organic resin, it is possibleto improve the adhesiveness of the shielding film formed on the filmowing to surface reforming.

It is also possible to form not only the shielding film but otherconnection wiring lines by using the aluminum film containing titanium.For example, connecting wiring lines for connecting circuits in thedriver circuit can be formed. However, in that case, it is necessary toform a contact hole in the third interlayer insulating film prior tofilm formation with a raw material for forming the shielding film or theconnecting wiring line.

Next, an oxide 3169 with a thickness of 20 to 100 nm (preferably 30 to50 nm) is formed on the surface of the shielding film 3168 by an anodicoxidation method or a plasma oxidation method (in this embodiment,anodic oxidation method). In this embodiment, since the film mainlycontaining aluminum is used as the shielding film 3168, an aluminumoxide film (alumina film) is formed as the anodic oxide 3169.

At this anodic oxidation treatment, an ethylene glycol tartrate solutionwith a sufficiently low alkaline ion concentration is prepared. This isa mixture solution in which an ammonium tartrate aqueous solution of 15%and ethylene glycol are mixed at 2:8, and ammonia water is added to thissolution to make adjustment so that pH becomes 7±0.5. Then a platinumelectrode as a cathode is provided in this solution, the substrate onwhich the shielding film 3168 is formed is immersed in the solution, anda constant (several mA to several tens mA) direct current is made toflow with the shielding film 3168 as an anode.

Although a voltage between the cathode and the anode in the solution waschanged with a lapse of time in accordance with the growth of an anodicoxide, the voltage is raised at a voltage rising rate of 100 V/min whilethe constant current is kept, and the anodic oxidation treatment isended when the voltage reached reachable voltage of 45V. In this way, itis possible to form an anodic oxide 3169 with a thickness of about 50 nmon the surface of the shielding film 3168. As a result, the thickness ofthe shielding film 3168 becomes 90 nm. Note that numerical valuesrelating to the anodic oxidation method shown here are merely examples,and optimum values can be naturally changed by the size and the like ofa component to be manufactured.

Besides, although such a structure is adopted here that the insulatingfilm is provided only on the surface of the shielding film by using theanodic oxidation method, the insulating film may be formed by a vaporphase method such as a plasma CVD method, a thermal CVD method, or asputtering method. In that case as well, it is preferable to set thefilm thickness to 20 to 100 nm (preferably 30 to 50 nm). Besides, asilicon oxide film, a silicon nitride film, a silicon nitride oxidefilm, a DLC (Diamond like carbon) film, or an organic resin film may beused. Further, a laminated film of a combination of these may be used.

Next, a contact hole reaching the drain wiring line 3165 is formed inthe third interlayer insulating film 3167 and the passivation film 3166,and a pixel electrode 3170 is formed. Note that pixel electrodes 3171and 3172 are pixel electrodes of adjacent different pixels,respectively. It is appropriate that in the case where a transmissiontype liquid crystal display device is formed, a transparent conductivefilm is used for the pixel electrodes 3170 to 3172, and in the casewhere a reflection type liquid crystal display device is formed, a metalfilm is used. Here, for the purpose of forming the transmission typeliquid crystal display device, an indium-tin oxide (ITO) film with athickness of 110 nm is formed by a sputtering method.

At this time, the pixel electrode 3170 and the shielding film 3168overlap with each other through the anodic oxide 3169, so that a holdingcapacitance (capacitance storage) 3173 is formed. In this case, it isdesirable that the shielding film 3168 is set at a floating state(electrically isolated state) or to a fixed potential, preferably to acommon potential (intermediate potential of an image signal transmittedas data).

In this way, an active matrix substrate including the driver circuit andthe pixel portion on the same substrate is completed. In FIG. 17(C), ap-channel TFT 3301, and n-channel TFTs 3302 and 3303 are formed in thedriver circuit, and a pixel TFT 3304 made of an n-channel TFT is formedin the pixel portion.

In the p-channel TFT 3301 of the driver circuit, a channel formationregion 3201, a source region 3202, and a drain region 3203 are formed ofthe p-type impurity regions (a), respectively. However, actually, thereexists a region containing phosphorus with a concentration of 1×10²⁰ to1×10²¹ atoms/cm³ in a part of the source region or drain region.Besides, in that region, there exists a catalytic element gettered inthe step of FIG. 17(B) and having a concentration of 5×10¹⁸ atoms/cm³ ormore (representatively, 1×10¹⁹ to 5×10²⁰ atoms/cm³).

In the n-channel TFT 3302, a channel formation region 3204, a sourceregion 3205, a drain region 3206, and a region 3207 disposed at one sideof the channel formation region (drain region side) and overlapping withthe gate wiring line through the gate insulating film (in thisembodiment, such a region is referred to as a Lov region. The “ov” isaffixed to denote “overlap”) are formed. At this time, the Lov region3207 contained phosphorus with a concentration of 2×10¹⁶ to 5×10¹⁹atoms/cm³, and is formed to totally overlap with the gate wiring line.

In the n-channel TFT 3303, a channel formation region 3208, a sourceregion 3209, a drain region 3210, and LDD regions 3211 and 3212 on bothsides of the channel formation region are formed. In this structure,since a part of the LDD regions 3211 and 3212 is disposed to overlapwith the gate wiring line, a region (Lov region) which overlaps with thegate wiring line through the gate insulating film and a region whichdoes not overlap with the gate wiring line (in this embodiment, such aregion will be referred to as Loff region. The “off” is affixed todenote “offset”) are realized.

A sectional view shown in FIG. 19 is an enlarged view showing the statein which manufacture of the n-channel TFT 3303 shown in FIG. 17(C)proceeds up to the step of FIG. 17(B). As shown here, the LDD region3211 can be divided into a Lov region 3211 a and a Loff region 3211 b.While the Lov region 3211 a contains phosphorus with a concentration of2×10¹⁶ to 5×10¹⁹ atoms/cm³, the Loff region 3211 b contains phosphoruswith a concentration 1 to 2 times (representatively 1.2 to 1.5 times) ashigh as that.

In the pixel TFT 3304, channel formation regions 3213 and 3214, a sourceregion 3215, a drain region 3216, Loff regions 3217 to 3220, and ann-type impurity region (a) 3221 being in contact with the Loff regions3218 and 3219 are formed. At this time, the source region 3215 and thedrain region 3216 are formed of the n-type impurity regions (a)respectively, and the Loff regions 3217 to 3220 are formed of the n-typeimpurity regions (c).

In this embodiment, the structure of a TFT forming each circuit isoptimized in accordance with a circuit specification required by thepixel portion and the driver circuit, and it is possible to improve theoperation performance and reliability of the semiconductor device.Specifically, in the n-channel TFT, the arrangement of the LDD region ismade different in accordance with the circuit specification, and one ofthe Lov region and the Loff region is appropriately used, so that a TFTstructure in which importance is attached to high speed operation or hotcarrier measures, or a TFT structure in which importance is attached tolow off current operation are realized.

For example, in the case of an active matrix type liquid crystal displaydevice, the n-channel TFT 3302 is suitable for a driver circuit such asa shift register circuit, a frequency dividing circuit, a signaldividing circuit, a level shifter circuit, and a buffer circuit, inwhich importance is attached to high speed operation. That is, the Lovregion is disposed at only one side (drain region side) of the channelformation region, so that such a structure is formed that a resistancecomponent is reduced to the utmost degree and importance is attached tohot carrier measures. This is because in the case of the foregoingcircuit group, the functions of the source region and the drain regionare not different from each other, and the direction of movement ofcarriers (electrons) is constant. However, as the need arises, the Lovregion can be disposed at both sides of the channel formation region.

The n-channel TFT 3303 is suitable for a sampling circuit (sample-holdcircuit) in which importance is attached to both hot carrier measuresand low off current operation. That is, the Lov region is disposed asthe hot carrier measures, and the Loff region is disposed to realize thelow off current operation. In the sampling circuit, the functions of thesource region and the drain region are inverted and the moving directionof carriers is changed by 180°, so that it is necessary to make such astructure that axial symmetry is established with respect to the gatewiring line. Note that according to circumstances, there can be a casewhere only the Lov region exists.

The n-channel TFT 3304 is suitable for the pixel portion and thesampling circuit (sample-hold circuit) in which importance is attachedto low off current operation. That is, the Lov region which can become afactor to increase an off current value is not disposed, but only theLoff region is disposed so that the low off current operation isrealized. Besides, the LDD region with a concentration lower than thatof the LDD region of the driver circuit is used as the Loff region, sothat such measures are adopted that even if an on current value islowered a little, an off current is thoroughly lowered. Further, it hasbeen ascertained that the n-type impurity region (a) 3221 is veryeffective in lowering an off current value.

It is appropriate that as against the channel length of 3 to 7 μm, thelength (width) of the Lov region 3207 of the n-channel TFT 3302 is 0.5to 3.0 μm, representatively 1.0 to 1.5 μm. Besides, it is appropriatethat the length (width) of the Lov regions 3211 a and 3212 a of then-channel TFT 2303 is 0.5 to 3.0 μm, representatively 1.0 to 1.5 μm, andthe length (width) of the Loff regions 3211 b and 3212 b is 1.0 to 3.5μm, representatively 1.5 to 2.0 μm. Besides, it is appropriate that thelength (width) of the Loff regions 3217 to 3220 provided in the pixelTFT 3304 is 0.5 to 3.5 μm, representatively 2.0 to 2.5 μm.

Further, one of the features of the present invention is that thep-channel TFT 3301 is formed in a self-aligning manner, and then-channel TFTs 3302 to 3304 are formed in a non-self-aligning manner.

Besides, in this embodiment, an alumina film with a relative dielectricconstant of as high as 7 to 9 is used as the dielectric of the holdingcapacitance, so that it is possible to reduce an area for formingrequired capacitance. Moreover, the shielding film formed on the pixelTFT functions as one of electrodes of the holding capacitance as in thisembodiment, so that it is possible to improve the opening ratio of animage display portion of an active matrix type liquid crystal displaydevice.

Note that the present invention is not necessarily limited to thestructure of the holding capacitance shown in this embodiment. Forexample, the structure of a holding capacitance disclosed in JapanesePatent Application No. Hei 9-316567 or No. Hei 10-254097 by the presentapplicant can also be used.

As shown in FIG. 18, an oriented film 3401 is formed on the substrate inthe state of FIG. 17(C). In this embodiment, a polyimide film was usedas the oriented film. A transparent conductive film 3403 and an orientedfilm 3404 are formed on an opposite substrate 3402. A color filter and ashielding film may be formed on the opposite substrate as the needarises.

Next, after the oriented film is formed, a rubbing treatment is appliedso that liquid crystal molecules are oriented with some uniform pre-tiltangle. Then the active matrix substrate on which the pixel portion andthe driver circuit are formed is bonded to the opposite substrate by awell-known cell assembling step through a sealing material, a spacer(both not shown), and the like. Thereafter, a liquid crystal 3405 wasinjected between the substrates, and they are completely sealed with anend-sealing material (not shown). It is appropriate that a well-knownliquid crystal material is used as the liquid crystal. In this way, theactive matrix type liquid crystal display device as shown in FIG. 18 iscompleted.

Next, the structure of this active matrix type liquid crystal displaydevice will be described with reference to a perspective view of FIG.21. For the purpose of making FIG. 20 correspond to sectional structuralviews of FIGS. 15 to 17, common reference symbols are used. An activematrix substrate is constituted of a pixel portion 3601, a scanning(gate) signal driver circuit 3602, and an image (source) signal drivercircuit 3603, which are formed on a glass substrate 3101. A pixel TFT3304 of the pixel portion is an n-channel TFT, and the driver circuitprovided on the periphery is constituted of a CMOS circuit as a base.The scanning signal driver circuit 3602 and the image signal drivercircuit 3603 are connected to the pixel portion 3601 through a gatewiring line 3124 and a source wiring line 3161, respectively. Besides,there are provided connection wiring lines 3606 and 3607 extending froman external input/output terminal 3605 to which an FPC 3604 is connectedto an input/output terminal of the driver circuit.

Embodiment 7

A CMOS circuit and a pixel matrix circuit formed through carrying outthe present invention applied to various display apparatuses (an activematrix type liquid crystal display, an active matrix type El display andactive matrix type EC display). Namely, the present invention may beapplicable to all the electronic equipments that incorporate thosedisplay devices as the display medium.

As such an electronic equipment, a video camera, a digital camera, aprojector (rear-type projector or front-type projector), a head mountdisplay (goggle-type display), a navigation system for vehicles, apersonal computer, and a portable information terminal (a mobilecomputer, a cellular phone, or an electronic book, etc.) may beenumerated. Examples of those are shown in FIGS. 23 to 24.

FIG. 23(A) shows a personal computer comprising a main body 2001, animage inputting unit 2002, a display device 2003, and a key board 2004.The present invention is applicable to the image inputting unit 2002,the display device 2003, and other signal control circuits.

FIG. 23(B) shows a video camera comprising a main body 2101, a displaydevice 2102, a voice input unit 2103, an operation switch 2104, abattery 2105, and an image receiving unit 2106. The present invention isapplicable to the display device 2102, the voice input unit 2103, andother signal control circuits.

FIG. 23(C) shows a mobile computer comprising a main body 2201, a cameraunit 2202, an image receiving unit 2203, an operation switch 2204, and adisplay device 2205. The present invention is applicable to the displaydevice 2205 and other signal control circuits.

FIG. 23(D) shows a goggle-type display comprising a main body 2301, adisplay device 2302 and an arm portion 2303. The present invention isapplicable to the display device 2302 and other signal control circuits.

FIG. 23(E) shows a player that employs a recoding medium in whichprograms are recorded (hereinafter referred to as recording medium), andcomprises a main body 2401, a display device 2402, a speaker unit 2403,a recording medium 2404, and an operation switch 2405. Note that thisplayer uses as the recoding medium a DVD (digital versatile disc), a CDand the like to serve as a tool for enjoying music or movies, forplaying games and for connecting to the Internet. The present inventionis applicable to the display device 2402 and other signal controlcircuits.

FIG. 23(F) shows a digital camera comprising a main body 2501, a displaydevice 2502, an eye piece section 2503, an operation switch 2504, and animage receiving unit (not shown). The present invention is applicable tothe display device 2502 and other signal control circuits.

FIG. 24(A) shows a front-type projector comprising a display device 2601and a screen 2602. The present invention is applicable to the displaydevice and other signal control circuits.

FIG. 24(B) shows a rear-type projector comprising a main body 2701, adisplay device 2702, a mirror 2703, and a screen 2704. The presentinvention is applicable to the display device and other signal controlcircuits.

FIG. 24(C) is a diagram showing an example of the structure of thedisplay devices 2601 and 2702 in FIGS. 24(A) and 24(B). The displaydevice 2601 or 2702 comprises a light source optical system 2801,mirrors 2802 and 2804 to 2806, a dichroic mirror 2803, a prism 2807, aliquid crystal display device 2808, a phase difference plate 2809 and aprojection optical system 2810. The projection optical system 2810consists of an optical system including a projection lens. Thisembodiment shows an example of “three plate type”, but not particularlylimited thereto. For instance, the invention may be applied also to“single plate type”. Further, in the light path indicated by an arrow inFIG. 24(C), an optical system such as an optical lens, a film having apolarization function, a film for adjusting a phase difference, an IRfilm may be provided on discretion of a person who carries out theinvention.

FIG. 24(D) is a diagram showing an example of the structure of the lightsource optical system 2801 in FIG. 24(C). In this embodiment, the lightsource optical system 2801 comprises a reflector 2811, a light source2812, 2813 and 2814, a polarizing converter element 2815 and acollimator lens 2816. Note that the light source optical system shown inFIG. 24(D) is an example and not particularly limited thereto. Forexample, in the light source optical system, an optical system such asan optical lens, a film having a polarization function, a film foradjusting a phase difference, and an IR film may be provided ondiscretion of a person who carries out the invention.

As described above, the scope of application of the semiconductor deviceof the present invention is very wide, and the invention can be appliedto electronic equipments of any fields. The electronic equipment of thisembodiment can be realized even if any combination of Embodiments 1 to17 is used.

EFFECT OF THE INVENTION

According to the present invention, uniform laser annealing becamepossible over the whole surface of the processed substrate. As a result,the characteristics of the semiconductor device within the substratesurface could be made uniform. In addition, the area of the laser beamto be irradiated on the surface to be formed can be made enlarge,thereby being capable of improving the productivity thereof.

Accordingly, in the case where an active matrix type liquid crystaldisplay device, for example, is manufactured while employing the TFTsmanufactured using the present invention, the display device with lessstripe due to laser processing could be obtained compared to theconventional ones.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[FIG. 1] A photograph of a silicon film that has been irradiated with aconventional linear laser beam.

[FIGS. 2A-2C] Views schematically showing FIG. 1.

[FIG. 3] A view showing a conventional optical system and optical pathfor forming a linear laser beam.

[FIGS. 4A-4B] Views showing laser beams entering into the conventionaloptical system in which laser beam is divided.

[FIG. 5] A view showing a conventional optical system and optical pathfor forming a linear laser beam.

[FIG. 6] A view showing an optical system and optical path according tothe present invention, for forming a linear laser beam.

[FIG. 7] A view showing an optical system and optical path according tothe present invention, for forming a linear laser beam.

[FIG. 8] A schematic view of an laser irradiation apparatus.

[FIGS. 9A-9C] Sectional views of the energy distributions of linearlaser beams in the width directions.

[FIG. 10] A photograph of a silicon film that has been irradiated with alinear laser beam according to the present invention.

[FIG. 11] A view schematically showing FIG. 10.

[FIG. 12] A view showing a laser irradiation system according to thepresent invention.

[FIG. 13] A view showing an optical system and optical path according tothe present invention, for forming a linear laser beam.

[FIG. 14] A view showing an optical system and optical path according tothe present invention, for processing a laser beam into square shape.

[FIGS. 15A-15F] Views showing manufacturing steps of a pixel circuit anda control circuit.

[FIGS. 16A-16F] Views showing manufacturing steps of a pixel circuit anda control circuit.

[FIGS. 17A-17C] Views showing manufacturing steps of a pixel circuit anda control circuit.

[FIG. 18] A sectional structural view of an active matrix type liquidcrystal display device.

[FIG. 19] A view showing an LDD structure of an n-channel TFT.

[FIG. 20] A perspective view of an active matrix type liquid crystaldisplay device.

[FIG. 21] A view showing an optical system having no reflecting mirror.

[FIG. 22] A view showing an optical system in which a position of areflecting mirror to be brought in, is changed.

[FIGS. 23A-23F] Views showing examples of electronic equipments to whichthe present invention is applied.

[FIGS. 24A-24D] Views showing examples of projectors to which thepresent invention is applied.

1. A method of fabricating a semiconductor device comprising: removingat least one edge of a first laser beam, thereby forming a second laserbeam having a straight line extending in a first direction; dividing thesecond laser beam in a second direction vertical to the first directionby passing the second laser beam through a cylindrical lens groupcomprising a plurality of cylindrical lenses so that the straight lineis parallel with the boundaries between the cylindrical lenses of thecylindrical lens group; condensing the divided laser beams; andirradiating a semiconductor film with the condensed laser beam.
 2. Amethod according to claim 1, wherein said first laser beam is selectedfrom the group consisting of KrF, XeCl, ArF, KrCl, Ar, YAG, and CO₂laser beams.
 3. A method according to claim 1, wherein said removing isperformed by using a slit.
 4. A method according to claim 3, wherein theslit comprises a material selected from the group consisting of glass,quartz ground glass, ceramic, and metal.
 5. A method according to claim1, wherein said semiconductor film is crystallized by said irradiatingwith the condensed laser beam.
 6. A method according to claim 1, whereinimpurities in said semiconductor film are activated by said irradiatingwith the condensed laser beam.
 7. A method according to claim 1, whereinsaid condensing is performed using at least one of a triplet typesymmetrical lens and a Tessar type symmetrical lens.
 8. A methodaccording to claim 1, wherein said semiconductor device is an electronicequipment selected from the group consisting of a video camera, adigital camera, a rear-type projector, a front-type projector, a headmount display, a goggle-type display, a navigation system for vehicles,a personal computer, a portable information terminal, a mobile computer,a cellular phone, and an electronic book.
 9. A method of fabricating asemiconductor device comprising: removing at least one edge of a laserbeam, thereby forming a second laser beam having a straight lineextending in a first direction; dividing the second laser beam in asecond direction vertical to the first direction by passing the secondlaser beam through a cylindrical lens group comprising a plurality ofcylindrical lenses so that the straight line is coincident with theboundaries between the cylindrical lenses of the cylindrical lens group;condensing the divided laser beams; and irradiating a semiconductor filmwith the condensed laser beam.
 10. A method according to claim 9,wherein said first laser beam is selected from the group consisting ofKrF, XeCl, ArF, KrCl, Ar, YAG, and CO₂ laser beams.
 11. A methodaccording to claim 9, wherein said removing is performed by using aslit.
 12. A method according to claim 11, wherein the slit comprises amaterial selected from the group consisting of glass, quartz groundglass, ceramic, and metal.
 13. A method according to claim 9, whereinsaid condensing is performed using at least one of a triplet typesymmetrical lens and a Tessar type symmetrical lens.
 14. A methodaccording to claim 9, wherein said semiconductor film is crystallized bysaid irradiating with the condensed laser beam.
 15. A method accordingto claim 9, wherein impurities in said semiconductor film are activatedby said irradiating with the condensed laser beam.
 16. A methodaccording to claim 9, wherein said semiconductor device is an electronicequipment selected from the group consisting of a video camera, adigital camera, a rear-type projector, a front-type projector, a headmount display, a goggle-type display, a navigation system for vehicles,a personal computer, a portable information terminal, a mobile computer,a cellular phone, and an electronic book.
 17. A method according toclaim 9, wherein the removing is performed by using both ends of thecylindrical lenses in the cylindrical lens group, the both ends of thecylindrical lenses comprising quartz ground glass.
 18. A method offabricating a semiconductor device comprising: removing at least oneedge of a first laser beam, thereby forming a second laser beam having astraight line extending in a first direction; dividing the second laserbeam in a second direction vertical to the first direction by passingthe second laser beam through a cylindrical lens group comprising aplurality of cylindrical lenses so that the straight line is parallelwith the boundaries between the cylindrical lenses of the cylindricallens group; condensing the divided laser beams; and scanning asemiconductor film with the condensed laser beam in the seconddirection.
 19. A method according to claim 18, wherein said first laserbeam is selected from the group consisting of KrF, XeCl, ArF, KrCl, Ar,YAG, and CO₂ laser beams.
 20. A method according to claim 18, whereinsaid removing is performed by using a slit.
 21. A method according toclaim 20, wherein the slit comprises a material selected from the groupconsisting of glass, quartz ground glass, ceramic, and metal.
 22. Amethod according to claim 18, wherein said condensing is performed usingat least one of a triplet type symmetrical lens and a Tessar typesymmetrical lens.
 23. A method according to claim 18, wherein saidsemiconductor film is crystallized by said scanning with the condensedlaser beam.
 24. A method according to claim 18, wherein impurities insaid semiconductor film are activated by said scanning with thecondensed laser beam.
 25. A method according to claim 18, wherein saidsemiconductor device is an electronic equipment selected from the groupconsisting of a video camera, a digital camera, a rear-type projector, afront-type projector, a head mount display, a goggle-type display, anavigation system for vehicles, a personal computer, a portableinformation terminal, a mobile computer, a cellular phone, and anelectronic book.
 26. A method of fabricating a semiconductor devicecomprising: removing at least one edge of a first laser beam, therebyforming a second laser beam having a straight line extending in a firstdirection; dividing the second laser beam in a second direction verticalto the first direction by passing the second laser beam through acylindrical lens group comprising a plurality of cylindrical lenses sothat the straight line is coincident with the boundaries between thecylindrical lenses of the cylindrical lens group; condensing the dividedlaser beams; and scanning a semiconductor film with the condensed laserbeam in the second direction.
 27. A method according to claim 26,wherein said first laser beam is selected from the group consisting ofKrF, XeCl, ArF, KrCl, Ar, YAG, and CO₂ laser beams.
 28. A methodaccording to claim 26, wherein said removing is performed by using aslit.
 29. A method according to claim 28, wherein the slit comprises amaterial selected from the group consisting of glass, quartz groundglass, ceramic, and metal.
 30. A method according to claim 26, whereinsaid semiconductor film is crystallized by said scanning with thecondensed laser beam.
 31. A method according to claim 26, whereinimpurities in said semiconductor film are activated by said scanningwith the condensed laser beam.
 32. A method according to claim 26,wherein said condensing is performed using at least one of a triplettype symmetrical lens and a Tessar type symmetrical lens.
 33. A methodaccording to claim 26, wherein said semiconductor device is anelectronic equipment selected from the group consisting of a videocamera, a digital camera, a rear-type projector, a front-type projector,a head mount display, a goggle-type display, a navigation system forvehicles, a personal computer, a portable information terminal, a mobilecomputer, a cellular phone, and an electronic book.
 34. A methodaccording to claim 26, wherein the removing is performed by using bothends of the cylindrical lenses in the cylindrical lens group, the bothends of the cylindrical lenses comprising quartz ground glass.
 35. Amethod of fabricating a semiconductor device comprising: removing atleast one edge of a first laser beam by using a slit, thereby forming asecond laser beam having a straight line extending in a first direction;dividing the second laser beam in a second direction vertical to thefirst direction by passing the second laser beam through a cylindricallens group comprising a plurality of cylindrical lenses so that thestraight line is parallel with the boundaries between the cylindricallenses of the cylindrical lens group; condensing the divided laserbeams; and irradiating a semiconductor film with the condensed laserbeam.
 36. A method of fabricating a semiconductor device comprising:removing at least one edge of a laser beam, thereby forming a secondlaser beam having a straight line extending in a first direction;dividing the second laser beam in a second direction vertical to thefirst direction by passing the second laser beam through a cylindricallens group comprising a plurality of cylindrical lenses so that thestraight line is coincident with the boundaries between the cylindricallenses of the cylindrical lens group; condensing the divided laserbeams; and irradiating a semiconductor film with the condensed laserbeam.
 37. A method of fabricating a semiconductor device comprising:removing at least one edge of a first laser beam by using a slit,thereby forming a second laser beam having a straight line extending ina first direction; dividing the second laser beam in a second directionvertical to the first direction by passing the second laser beam througha cylindrical lens group comprising a plurality of cylindrical lenses sothat the straight line is parallel with the boundaries between thecylindrical lenses of the cylindrical lens group; condensing the dividedlaser beams; and scanning a semiconductor film with the condensed laserbeam in the second direction.
 38. A method of fabricating asemiconductor device comprising: removing at least one edge of a firstlaser beam by using a slit, thereby forming a second laser beam having astraight line extending in a first direction; dividing the second laserbeam in a second direction vertical to the first direction by passingthe second laser beam through a cylindrical lens group comprising aplurality of cylindrical lenses so that the straight line is coincidentwith the boundaries between the cylindrical lenses of the cylindricallens group; condensing the divided laser beams; and scanning asemiconductor film with the condensed laser beam in the seconddirection.
 39. A method according to any one of claims 35 to 38, whereinsaid first laser beam is selected from the group consisting of KrF,XeCl, ArF, KrCl, Ar, YAG, and CO₂ laser beams.
 40. A method according toany one of claims 35 and 36, wherein said semiconductor film iscrystallized by said irradiating with the condensed laser beam.
 41. Amethod according to any one of claims 35 and 36, wherein impurities insaid semiconductor film are activated by said irradiating with thecondensed laser beam.
 42. A method according to any one of claims 35 to38 wherein said condensing is performed using at least one of a triplettype symmetrical lens and a Tessar type symmetrical lens.
 43. A methodaccording to any one of claims 35 to 38, wherein said semiconductordevice is an electronic equipment selected from the group consisting ofa video camera, a digital camera, a rear-type projector, a front-typeprojector, a head mount display, a goggle-type display, a navigationsystem for vehicles, a personal computer, a portable informationterminal, a mobile computer, a cellular phone, and an electronic book.44. A method according to any one of claims 36 and 38, wherein theremoving is performed by using both ends of the cylindrical lenses inthe cylindrical lens group, the both ends of the cylindrical lensescomprising quartz ground glass.
 45. A method according to any one ofclaims 35 to 38, wherein the slit comprises a material selected from thegroup consisting of glass, quartz ground glass, ceramic, and metal. 46.A method according to any one of claims 9, 26, 36 and 38, wherein thecylindrical lens group is shorter than the width of the laser beam. 47.A method according to any one of claims 37 and 38, wherein saidsemiconductor film is crystallized by said scanning with the condensedlaser beam.
 48. A method according to any one of claims 37 and 38,wherein impurities in said semiconductor film are activated by saidscanning with the condensed laser beam.